Spark plug



Sept. 27, 1949. 1 F. WINHOLM 2,483,357

I SPARK PLUG Filed July 16, 1945 3 Sheets-Sheet l m .rm

Patented Sept. 27, 1949 UNITED STATES PATENT OFFICE SPARK PLUG Application July 16, 1945, Serial No. 605,270 In Sweden August 30, 1944 3 Claims.

The present invention refers to a sparkplug comprising a number of substantially concentric electrodes insulated. from each other by means of one or more separating bodies of preferably oeramic insulating material, said electrodes bein adapted to be coupled in series with a potential source in an electric oscillation circuit.

The invention is generally characterized by the fact, that the electrodes possess great mutual surface capacities substantially in the axial direction of the sparkplug, whereby the end of the center electrode intended for sparking is substantially enlarged in order upon oscillatory charging of said surface capacities to generate instant super-potentials considerably higher in the respective spark gaps than the applied potential, for ionizing existing gas between the electrodes and to prepare and facilitate an effective sparking between said electrodes.

The invention is particularl effective in sparkplugs provided with one or more intermediate concentric electrodes. The spark-plugs of this invention shall preferably be connected to an oscillating circuit of low damping characteristics, whereby the present sparkplug alone or in coma vbina-tion with the said oscillator circuit will give a substantially superior sparking compared to known sparkplugs.

The present invention particularly relates to sparkplugs for combustion engines. The invention substantially widens the conditions within which a sparkplug can satisfactorily work, and the efliciency of the sparkplug in heavily loaded combustion engines is substantially increased.

Known sparkplugs have the disadvantage that they normally operate only within narrow temperature limits, and that they cannot sustain continuous operation at high load.

Many combustion engines of modern construction are called hot engines, because a high temperature is sustained in the combustion chamber. In such engines it often happens that those parts of a sparkplug, which are not sufiiciently cooled, will keep a temperature above the ignition temperature of the combustion vapours and therefore cause a Dre-ignition. For such engines so-called cold spark-plugs are used, and which keep a sufficiently low temperature. These sparkplugs are, however, suitable only for hot engines and do not operate in cold engines, because its low mean temperature is not sufiiciently high to burn carbon and soot eventually deposited on the insulating parts of the sparkplug, and which might cause shortcircuits between the electrodes.

Whether a known s-parkplug should be called hot or cold depends on the surfaces and the masses of those parts of the electrodes and of the surrounding insulating material, which are iQosed to the hot combustion gases in the combustion chamber.

The requisites which are now given for hot and cold sparkplugs are contrary to each other, because a sparkplug must reach a certain minimum temperature in order to keep clean, while the same sparkplug should not exceed a certain temperature order to prevent pre-ignition, and a rapid destruction of the sparkplug. At present there are a great number of difierent types of sparkplugs varying from the coldest to the hottest, and which are necessary in order to cover the entire field of operation of existing combustion engines.

Certain engines, for example those of high compression, of high revolutions for airplanes, racers, etc. have to have more than one kind of sparkplugs, because sparkplugs suitable for starting of the engine would be destroyed and cause pre-ignition at a high motor load, while at low load or at the start an ordinary cold spark-plug would refuse to cause ignition.

In order to prevent shortcircuits due to soot deposits between the usual two electrodes the sparkplug has sometimes been provided with a plurality of series coupled auxiliary or intermediate electrodes arranged in a straight line or in other manners, so that a spark will be distributed over all the sparkgaps. Such a sparkplug will operate as long as at least one gap is clean.

The disadvantage of known sparkplugs with intermediate electrodes, however, consists in the fact, that the electrodes have been cast together with and enclosed by the insulating material. Due to differences of the respective coefficients of expansion of the electrodes and of the insulatin material dangerous stresses occurred in the insulating material.

The intermediate electrodes of known constructions also lacked means for conducting heat away from the respective electrodes, on account of which said electrodes became too hot, thus causing pre-ignition and were rapidly destroyed.

The object of the present invention is to produce an improved sparkplug, which eliminates all of the above cited inconveniences of known sparkplugs, and which can meet the above mentioned contradictory requisites, so that to a great extent the same sparkplug can effectively operate over substantially varying loads in any given combustion engine.

Another object of the invention is to eliminate limitations of known sparkplugs with reto length of life and efficiency.

of ti and ..-.us providing said electrodes in a spark gap with a great surface capacity, a considerable advantage is obtained according to the present invention, and which consists in the fact that due to the great capacities a high initial pulse potential over each sparkgap is obtained even at a relatively low applied potential, due to the fact that the charge and discharge of the said surfaces and corresponding capacities is oscillatory. This feature is particularly noticeable when the oscillatory circuit has low damping characteristics.

By these oscillatory charges and discharges of the condenser surfaces of the electrodes so-called dark or luminous discharges can take place, due to the said super-potentials, b means of which the gas molecules existing between the respective electrodes are ionized, thereby preparing a sudden and immediate spark discharge through the ionized gas at the sparkgaps.

Only after a suitable ionization of a gas is it possible to produce a spark through said gas.

The center electrode has according to this invention its surface at the first sparkgap substantially enlarged compared to that of known sparkplugs, and the intermediate electrodes, when used, are provided with sleeves and/r collars of suitable height for facilitating the necessary conduction of heat to the outside of the sparkplug. The relatively large surfaces and corresponding capacities of the collars and sleeves of these intermediate electrodes contribute in a high degree to cause an ionization of the combustible gases before the spark. The greater the capacity, the greater will be the dark pro-discharges and the corresponding ionization.

l n there are a plurality of sparkgaps comprising inherent capacities coupled in series with t e oscillatory circuit, the total input potential is equal to the sum of the part-potentials over the gaps as long as no discharges take place, but as soon as discharges, even dark invisible ones, take place, the input potential will be less than the sum of all the then appearing part selectors.

By utilizing this principle of increased capacity on the central and intermediate electrodes a new and valuable technical effect is according to the present invention obtained.

In internal combustion engines of high compression, in which a spark is difficult to obtain, when usin ordinary sparkplugs, unless an extra high potential is applied, sparks are readily obtained by spark plugs manufactured according to this invention even when relatively low potentials are applied, and ionization and ignition of the gas can be obtained even at relatively high compression pressures.

According to the present invention the insulators between the respective electrodes are so arranged, that only a small part of their surfaces will be in direct contact with the hot combustion gases. For this reason ceramic insulators can be used also in so-called hot engines, such as high compression airplane engines and rapidly working automobile engines without impairing the glaze or the insulating material.

An effective cooling of the intermediate electrodes is obtained by means of the relatively high sleeves which are arranged on the said electrodes, and which can eventually extend outside or above the region of the correspondin cylinder block.

Spark plugs according to the present invention can therefore be used in both cold and hot engines.

On account of the large sparking surfaces of the central and intermediate electrodes a greater length of life is obtained, because corrosion need not take place at the same spot as in known sparkplugs, due to the fact that the spark can be distributed or occur at difierent places over extensive surfaces.

The powerful ignition preceded by ionization obtained between the electrodes according to this invention prevents soot and carbon deposits, because the powerful sparks and the regular ignitions cause sufficiently high temperatures in the combustion chamber and at the surface of the spark. plug so as to cause a complete combustion of soot eventually deposited in any of the sparkgaps.

Other advantages of the present invention are the following. Adjustment of the spark gaps is not needed, because the distance between the electrodes is determined by the dimensions of the component parts of the plug.

As the inner parts of the sparkplugs are hermetically sealed from the combustion gases, and only the sparking surfaces of the electrodes can contact the gases, the sparkplugs can easily be aept clean.

The invention will be more fully understood by the following description of some embodiments of the invention in connection with reference to the accompanying drawings, of which:

Fig. 1 is a vertical section of a section of a sparkplug provided with ringshaped intermediate electrode and heat-conducting sleeve.

Fig. 2 is a plan View of the underneath of sparkplug shown in Fig. 1.

Figs. 3 and 4 are vertical sections of other embodiments of the invention.

Figs. 5 and 6 are vertical sections on an enlarged scale of parts of sparkplugs embodying the invention.

Fig. '7 is a vertical section of a sparkplug according to the invention and provided with only two electrodes.

Fig. 8 is a vertical section of a, sparkplug for an airplane engine and provided with a radio screen.

Fig. 9 is a vertical section of the lower part of the sparkplug shown in Fig. 8 and showing that different heat conducting qualities can be obtained in the same sparkplug by only varying the length of the sleeve of the intermediate electrode.

Figs. 10 and 11 show vertical sections of part of other similar sparkplugs, whereby the shape of the electrodes have been given alternative forms.

The sparkplug shown in Fig. 1 comprises a casing 55 provided with threads for attachin to an engine block in known manner. The lower part of said casing serves as main electrode. The central electrode comprises the following parts: A central cylinder-shaped electrode l3 attached to a central bolt H, the upper end of which is provided with a nut 5 for holding together the several parts of the sparkplug. The upper part iii of the nut 5 is provided with another nut I 6 for attaching a cable from a, high tension potential source. Around the central electrode l3 there is arranged an intermediate electrode l, which forms ringshaped spark-gaps l2 and I4 between the center and main electrodes. The intermediate electrode is provided with a sleeve 2 concentrically arranged about the central electrode and separated from same by a preferably ceramic insulator 3. The sleeve 2 is provided with a collar 4 embracing the insulator it. The sleeve isso dimensioned, and arranged that. heat from, the inter-mediate elece trode s rapidly conducted from; they said electrode. The insulator 3 is provided with two, cylindrical outside: surfaces ct different diamet rs an nit d by conical surface.

Between the upper part of the, center electrode I! and the sleeve 2 of th intermediate. electrode I on. one side and th casing. I5 on the other side. there is provided an insula or I. W shers. 9 and I are provided between the insulator I and the, casin to prevent escape of pres ure. gases from the interior of. the combustion chamber. A nut. 6 is provided to secure the insulator 'I to the casing IS. A fireproof cement I9 is applied between the upper part of insulator a and the insulator I to prevent escape of gases along the sleeve 2 and collar 4..

The spark-plug which can be used for hi p sure engines, where an extra high applied volta e is needed, can be provided with an insulator petticoat 8 cemented to the insulator I by means of a cement layer 20. Between nut and the petticoat 8 the-re is provided a washer 2 I In Fig. 3. is shown a similar sparkplug provided with an insulator 31, a central electrode I3 and bolt H. An intermediate electrode I with sleeve 2 and collar 34 at about right angles to the walls of the sleeve is provided, said collar being adapted to embrace a shelf of the inner insulator 3, the upper more narrow part of which is hermetically sealed to the outside insulator 31 by a layer of cement 38.

In Fig. 4 is shown a spark plug provided with a rad o interference shield. The nut 0 of Fig. 3 has here been made in the form of a metallic shield it surrounding the whole upper part of insulator 41, in which a hollow nut 48 is located for holding together the center electrode and other parts of the sparkplug. The nut 48 is hollow and adapted to receive an electric cable for current supply.

The outside lower surface of the center electrode 53 is conically shaped to facilitate the agglomeration of any oil drops which might remain after stopping of the engine. The spark plug is provided with an interior insulator 43 separating the center electrode 51 from the intermediate electrode 5| and its sleeve 42 and collar 44. Between the insulators 43 and 4'Ithere is provided a cement 43. Between the nut 48 and the insulator 41 there is provided a washer 58.

In this embodiment the exposed sparking surfaces of the electrodes are conically shaped. Concentric sparkgaps 52 and 54 are arranged between the electrodes. Due to a somewhat lower height of the sleeve 42 of the intermediate electrode 5|, the sparkplug shown in Fig. 4 is slightly hotter than that shown in Fig. 3.

In order to increase the heat conduction from the central and intermediate electrodes the inner and/or exterior insulators 43 and 41 respectively can be made of insulating but heat-conducting material.

Figures 5 and 6 are each provided with two intermediate electrodes 63 and 65 respectively 61 and 69 arranged about a center electrode 6| respectively I8 with two extra sparkgaps 62 and 64.

In Fig. 5 the intermediate electrodes consist of concentric metal rings 63, 65 with upper collars against which insulators 62 and 64 respectively are arranged. A cement 66 serves as an upper sealing. In this embodiment \no particular electrodes and the insulator II are held together.

by a central bolt I8 in the same manner as shown n the other fi ure Fig. 7 shows a sparkplug of the simplest form according to the present invention being provided with only two electrodes. The center electrode 8| is provided with great surface in the spark gap proper and corresponding great capacity with respect to the other electrode, whereby the sparkgap 83 between the center electrode 8| and the surfaces of the casing I5 and lower part 84 form a condenser of relatively high capacity.

The other surfaces of the center electrode are also large and the center bolt 81 is provided with a cylindrical swelling 85 adjacent the electrode 8 I. The center electrode terminates in a point 82 so that fuel or oil not ignited in the engine after driving may collect at the point 82 and from there drop down into the cylinder. An insulating sleeve 86 insulates the electrodes down to the sparkgap so that the hot combustion gases will strike only a very little surface of the said insulator.

Fig. 8 is a spark plug for an airplane engine in which IIII is a central bolt, to which a center electrode I02 is attached. An intermediate electrode I04 provided with a conical sleeve I03 is provided and separated from the center bolt IN by means of a conical moulded insulator I06. Between the intermediate electrode I03 and the main electrode 5235 there is provided an insulator I01, which is held together with the intermediate electrode and insulator I05 by the bolt I0| and a nut H0. The sparkgaps I08 and I09 are here so shaped that no pockets exist between the electrodes, where soot or carbon can be deposited.

Fig. 9 is a magnified detail of the lower part of the sparkplug shown in Fig. 8, where particularly the right hand side shows smooth surfaces without any pockets in the spark gaps I08 and I03. At the left side there is shown an alternative construction, where shallow annular gaps 208 and 209 between the oppositely situated discharge surfaces of the respective electrodes are located.

The sleeve of the intermediate electrode is conically shaped so that the manufacture of both the insulator I06 and the sleeve I03 is facilitated, due to their simple construction.

If different lengths of the sleeve I03 are desired as indicated by the dot-dash lines I--IV shown in the drawing, the other parts of the sparkplug are identical, and an intermediate sleeve of desired length can be inserted, depending upon, whether a somewhat warmer or cooler sparkplug is desired. The upper part between the sleeve I03, the conical form piece I06 and the insulator I0'I should be filled with an insulating cement III.

Figs. 10 and l 1 show two alternative arrangements of the electrodes and the lower part of the insulating form pieces different from those shown in Figs. 8-9.

In Figs. 10-11 the active sparking surfaces of the electrodes are rounded without any sharp lines or corners. By rounded corners a better potential charge is built up on the respective electrodes for ionizing action and posterior sudden discharges.

In Fig. 10 the center electrode 3Ul392 and the intermediate electrode 304 with the respective insulators 388 and 397 are placed within the casing of the sparkplug, so that a separate sparking chamber is formed within the sparkplug into which the fuel gases easily can gain access. In this manner the sparkplug does not need to protrude into the combustion chamber and will always be out of the way of the piston or a cylinder. The sparkgaps 308 and 309 are ring-shaped and fairly open to prevent deposition of soot and to facilitate cleaning.

In 11 the center electrode 455 and the intermediate electrode 69 are similarly arranged those shown in Fig. 10 with the exception that the lower surface of the interior insulator 4% is conical in order to allow the electrode head partly to sink into the conical depression of the said in sulator. The lower suriace of the insulator 4B? is also slightly conically shaped to fit the shape of the intermediate electrode.

Fig. 11 offers the advantage of electrodes with rounded corners on the active discharge surfaces and substantially no pockets in which soot can be deposited, and which might cause short circuits. Nevertheless the electrodes in Fig. 11 are all located at about the same level, but haveo'pen discharge spaces so arranged between the respective electrodes, that soot and carbon deposits between the electrodes will be substantially prementedv Similar constructions are aiso shown in Figures 8-10 and 6.

What I claim is:

l. A sparkplug for igniting combustible gases comprising a central electrode having a cylindrical stem and a sparking head of large diameter with respect to the diameter of the stem, a concentric exterior electrode and a concentric intermediate electrode, said electrodes being electrically insulated from each other by means of molded ceramic insulators, in which the adjacent surfaces of each pair of adjacent electrodes constitute concentrically arranged surfaces including sparking surfaces, the areas of said surfaces being so chosen as to form with the air spaces between said sparking surfaces condensers of such capacity that, when a source of high potential is applied between the central and exterior electrodes, an oscillatory charge is produced, the maximum potential of which is greater than the potential applied between the central and exterior electrodes, and in which the intermediate electrode comprises a short heat conducting metallic sleeve for cooling purposes, the length of said sleeve being substantially shorter than that of the exterior electrode and so arranged in close contact with the surrounding insulators, that the sparkplug when in use attains the correct temperature for efiicient operation.

2. The sparkplug claimed in claim 1, in which the said heat conducting metallic sleeve is conical, a conical ceramic insulator being fitted between adjacent interior and exterior electrodes and of a length substantially greater than that of the heat conducting sleeve.

3. A sparkplug for igniting combustible gases comprising a central electrode having a cylindrical stem and a sparking head of large size with respect to the diameter of the stem, and a concentric exterior electrode, said electrodes being electrically insulated from each other by means of an insulating molded insulator, in which adjacent surfaces of the central and exterior electrodes constitute concentrically arranged surfaces including sparking surfaces, the areas of said surfaces being so chosen as to form with the air spaces between said sparking surfaces condensers of such capacity that, when a source of high potential is applied between the central and exterior electrodes, anoscillatory charge is produced, the maximum potential of which is greater than the potential applied between the central and exterior electrodes.

FOLKE WINHOLM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

